Solve by tecnically or logically.
Logical way :-
If Rs 100 = 100%,
then for 100% of Rs 400/- = Rs 4.
So for Rs 100/- , it will be 25%
Now coming to the question, They have brought the table for Rs 400/- and sold it for Rs 500/- , it is clear that it was a profit.
So if Rs 100/- = 25% , then for Rs 500/- , it will be (25% * 5) = 125% .
Therefore, 25% gain is the answer.